The present invention relates to an apparatus for monitoring the air pressure of a tire for an automobile, and more particularly, to a semiconductor sensor for use in such a monitoring apparatus.
A wireless communication type tire monitoring apparatus for monitoring the condition of a plurality of vehicle tires from a passenger compartment is known in the prior art. The tire monitoring apparatus of the prior art includes a transmitter provided for each vehicle tire to transmit a signal indicating the air pressure of the tire. The tire monitoring apparatus also includes a display for informing the automobile driver of the air pressure of each tire. The driver monitors from the passenger compartment whether the air pressure in each tire is appropriate.
Each transmitter includes an acceleration sensor for detecting whether the automobile is moving. The transmitter detects the air pressure and transmits the detection result only when the automobile is moving. This reduces unnecessary consumption of a primary battery that functions to supply power to the transmitter and prolongs the life of the primary battery.
The transmitter has a circuit board. A microcomputer and electronic components, which are used in a pressure sensor, an acceleration sensor, a primary sensor, a transmitting circuit, and an oscillation circuit, are connected to the circuit board. These devices are integrated to manufacture a relatively compact transmitter. Japanese Laid-Open Patent Publication No. 9-18017 describes a pressure sensor and an acceleration sensor of the prior art. Among the components of the transmitter, the pressure sensor and the acceleration sensor are relatively large. It was difficult to decrease the size of these sensors in the prior art.